Currently, in LTE (Long Term Evolution) and LTE-Advanced, which are becoming a mainstream as mobile communication systems, an orthogonal frequency division multiplexing (OFDM) scheme as a downlink signal waveform and a single carrier frequency-domain equalization (SC-FDE) scheme as an uplink signal waveform are used. In a 5-th generation mobile communication system (5G system), further improvement in frequency utilization efficiency is demanded. As a new signal waveform for realizing the improvement in the frequency utilization efficiency, research and development on a waveform shaping technology based on conventional schemes are in progress.
However, the conventional waveform shaping technology is mainly studied based on a downlink OFDM scheme, and there are few studies on an uplink SC-FDE scheme. The SC-FDE scheme has a feature that a peak-to-average power ratio (PAPR) is low as compared to the OFDM scheme, and can reduce a back off margin of a power amplifier mounted on a transmitter, and thus is very effective as a transmission waveform on a terminal side. On the other hand, the SC-FDE scheme has high out-of-band emission (OOBE), and, in terms of frequency utilization efficiency, OOBE suppression has been a problem to be solved.
In order to suppress out-of-band emission, a low pass filter (LPF) is effective. However, for example, in LTE, a guard bandwidth in a band is only about 0.25 MHz at most remaining on both sides. A large amount of calculation is required in order to mount an LPF that sufficiently suppresses out-of-band emission within this narrow guard band.
The inventors of the present application have proposed a universal time-domain windowed orthogonal frequency division multiplexing (UTW-OFDM) scheme regarding an OFDM (A) signal transmission device without using an LPF (see Patent Document 1).